How trees eat: An Introductory Guide to Photosynthesis

Published Thursday 19th February 2015

Trees, among other plant life, are responsible for making the planet habitable to oxygen-breathers like us.

But how did they achieve this amazing feat and how might humanity be able to make use of this unique process in the future? In this guide we'll delve into the world of photosynthesis and the science that powers plants.

A brief introduction

Photosynthesis describes the conversion of the energy from light into chemical energy. The majority of plants can photosynthesise, as can some types of bacteria and other cellular organisms.

For the process to take place, a green pigment called chlorophyll is required, as well as light, water and carbon dioxide.

The process

Photosynthesis tends to take place in the leaves of plants, where species store all the necessary ingredients for the process.

Water is transported to the leaves via the root system, which draws it from the ground. Carbon dioxide enters through pores in the leaves, known as stomata, and oxygen leaves the same way.

In the first step of the process, the chloroplasts inside the cells of the leaf taken in sunlight. When this solar energy is absorbed, it's used to make a type of nucleotide known as ATP (Adenosine Triphosphate).

This process - known as the 'light reaction' - is achieved by energising some of the electrons in the chlorophyll, freeing them from their molecular bonds. This leaves a space free for the electrons of the hydrogen atoms inside the water molecules, which become attracted to the chlorophyll.

The water molecules are no match for this strong attraction and break apart into their constituent parts of oxygen atoms, protons and electrons. Loose oxygen atoms then combine, forming free oxygen, which is released into the atmosphere.

Finally, the electrons and protons freed during the other stages interact in the cell, producing ATP and another compound known as NAPD.

The Dark Reaction

Despite their name, dark reactions (also referred to as the 'Calvin Cycle') don't have to take place at night. They simply don't require the presence of light to work.

In this part of the photosynthesis process, the chemical energy stored in the ATP and NAPD are used to create carbohydrates using the remaining hydrogen and carbon dioxide taken from the atmosphere to, typically, create glucose – a simple type of sugar (although a number of other compounds can be formed by this process).

Limits

How efficient the photosynthesis process is in any plant is reliant on several environmental factors, including the prevalence of light, water and carbon dioxide. If the plant's access to any of these is compromised, this can limit how effective it is at photosynthesising.

For instance, if the weather is dry or hot, the leaves of the plant might close their stomata to prevent water from evaporating. In cases like this, some plants begin a process called photorespiration – a metabolic process that aims to limit wasteful oxygenation.

Some plants, however, have adopted to this climate and keep high levels of carbon dioxide inside their cells to readily create glucose and prevent photorespiration.

Why is photosynthesis important?

Photosynthesis has shaped planet Earth into the planet we know today. Before life learned this neat trick, the atmosphere was mostly made up of carbon dioxide and other noxious gases emitted from volcanoes.

The photosynthesiers steadily cracked the carbon, producing oxygen that eventually build up in the atmosphere (although much remained locked up in rocks). The formation of oxygen also contributed to the development of the ozone layer as ultraviolet light split these molecules in the atmosphere.

We can directly attribute this development to ushering life out of the oceans and the development of respiration. And it's oxygen that keeps us alive today, offsetting the carbon dioxide produced by respiring organisms like us.

Hacking Photosynthesis

As well as figuring out just how this process works in recent years, scientists have also made great strides in tinkering with the process. This 'hacking' of photosynthesis has yielded promising results in preliminary studies.

Last year, scientists tinkered with a plant enzyme called Rubisco in an effort to try and enhance the process. By replacing a tobacco plant's natural genes with ones transplanted from cyanobacteria, the team from Cornell University were able to increase the rate of CO2 turnover.

While attempts to improve the efficiency of photosynthesis are still in the relatively early stages, the implications for the field are profound. With the planet's population expected to exceed nine billion by 2050 – higher crop yields made possible through the process could be a boon when it comes to making the most of limited agricultural space.

And You?

If you've got any questions about photosynthesis, or simply want to discuss this fascinating topic further, be sure to give us a shout on Twitter – we always want to hear what you have to say.

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Image used courtesy of Wikimedia Commons, kismoslek on Pixabay and Zappys Technological Solutions on Flickr.

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